The toxic effects of herbicides (Machete, Saturn) and pesticides (Diazinon and Malathion) on green algae, Scenedesmus obtusiusculus, and cyanobacteria, Anabaena flos aquae, were studied.
The results indicated that Machete and Saturn, in comparison to Diazinon and Malathion, were more toxic. On the other hand it was revealed that green algae was more sensitive to the pesticides than the cyanobacteria. When we added 3.199 mg/l machete (EC50 of this toxicant for Anabaena flos aquae) to a mix algal culture, the growth rate of green algae after 6 days of treatment was reduced 0.95 times, while it was 4.5 for the cyanobacteria. Treating the culture with 10.53 mg/l of Saturn for the same period of time revealed that the growth rate for green algae and the cyanobacteria increased 1.19 and 7 times, respectively. Hence, we can conclude that pesticides are capable of decreasing the diversity of the phytoplankton species in an aquatic ecosystem that from the fisheries point of view could cause serious problems.